Corn Rootworm Could Be Back Big This Year

The western corn rootworm, a Farm Belt scourge, is gaining further ground against genetically modified crops designed to kill it, marking a setback for biotech seed makers.

The rootworm, a voracious bug that can undermine farmers' crops, is developing resistance to pest-killing toxins in corn seed marketed in the U.S. by Syngenta AG of Switzerland, according to new research from Iowa State University.

The study, published last month, expands on earlier research showing that the insect had developed resistance to a widely grown genetically modified corn developed by Monsanto Co.

The more-resilient bugs, documented as showing resistance to the Syngenta product in Iowa cornfields, signal problems for farmers who rely heavily on biotech seeds to ward off pests and to save money on insecticides. The hardier insects also underline the challenges facing seed companies, which have sunk billions of dollars into developing high-tech crops that still can fall victim to insects and weeds that develop resistance to the most common methods of control.

"These data serve as an early warning to show the potential vulnerability," said the study's author, Iowa State entomologist Aaron Gassmann. He said it was too early to determine the scope of the problem, or how exactly the rootworms had developed resistance to the insect-killing proteins.

The research, published in the peer-reviewed Proceedings of the National Academy of Sciences, documented that some rootworms already resistant to Monsanto's widely used corn seed also were able to withstand Syngenta's Agrisure RW corn trait, which has been on the market since 2007.

Syngenta, which sells agricultural products and chemicals, said it was difficult to measure such resistance among corn rootworms, partly because of a lack of consensus among government officials, academics, and companies about how to define the resistance phenomenon.

However, "it is clear that there is increasing unexpected damage to corn crops from [corn rootworms] in certain areas with all traits, and that is a concern for everyone," said Chuck Lee, who heads Syngenta's North American corn business, in a written statement.

The company estimates that "unexpected damage" has occurred on just 0.2% of U.S. farm acres planted with corn varieties genetically modified to produce proteins to kill the insects, and that the affected areas had been planted repeatedly with corn each year instead of rotating in other crops, a tactic that can prevent corn-favoring pests from gaining a foothold.

Corn rootworms "should be considered a challenge to be managed, not a problem that can be solved," Mr. Lee said.

Seed companies more than a decade ago introduced the first corn capable of producing proteins that kill pests such as corn rootworms, but are harmless to mammals, birds, and most beneficial insects. Companies billed the seeds as a more efficient way to guard crops and minimize insecticide use. Last year, about 76% of U.S. corn acreage was planted with such genetically modified varieties, according to federal data.